Pressing pliers may serve for realizing general pressing purposes or for electric purposes. In the later case, they are also designated as crimping pliers. Depending on the design of the work piece to be pressed and crimped, respectively, substantial pressing forces have to be applied to attain a desired plastic deformation of a work piece, the work piece being introduced between pressing die halves or die halves of the pressing pliers. The amount of the required pressing force may depend on                the material of the work piece or of the work pieces when connecting a plurality of work pieces by pressing,        the dimensions or the diameter of the work piece, and/or        the plastic deformations desired during pressing.        
For introducing the work piece between the pressing dies of the pressing pliers, the pressing pliers possibly need to have a great opening width to be capable of surrounding the work piece to be pressed by the die halves in the open position, even if the work piece has comparatively great dimensions. At the beginning of the closing movement of the pressing pliers, the forces to be applied by the user of the pressing pliers are rather irrelevant until the die halves contact the work piece in the closed position. During the actual pressing step, the pressing forces to be applied are substantial, the pressing force even increasing during the continued closing movement.
Pressing pliers are known from German patent application No. DE 197 09 639 A1. The known pressing pliers include two hand levers being movable with respect to one another and being operable by one hand. Furthermore, the pliers include two pressing jaws which are commonly rotatable about a common joint. One of the pressing jaws is fixedly connected to one hand lever such that the pressing jaw and the hand lever form a fixed pressing pliers portion, while the other pressing jaw is pivotally connected to the fixed pressing pliers portion by the joint. The pressing pliers include divided die halves being located at the pressing jaws and forming a pressing die. The known pressing pliers include a forced locking mechanism for attaining a defined end position of the die halves. A pressure lever is pivotally connected between the two hand levers by additional joints, the pressure lever together with the movable hand lever forming a toggle lever drive. The two die halves are designed as one piece with the respective pressing jaw and as precision casting elements.
According to German patent No. DE 199 24 087 C2 corresponding to U.S. Pat. No. 6,289,712 B1, the die jaws are being inserted in the pressing jaws in a replaceable way. In this way, different die halves can be used in the same pliers for different work pieces. The die halves may be supported with respect to the pressing jaw with a clearance. In this way, a centering adaptation in the direction of the separation plane of the die halves is possible.
One drawback of the above described prior art pressing pliers is that there is a fixed dependency between the opening angle of the pressing jaws, on the one hand, and of the hand levers, on the other hand. The dependency is influenced by the toggle lever drive. Consequently, a maximum opened position of the pressing jaws results in a maximum opened position of the hand levers. This may be disadvantageous, for example, when the pressing pliers with the die halves have to be moved over a work piece when there only is little space. In some cases, this movement with the fully opened hand levers is not possible. Furthermore, when using the known pressing pliers, it has been found that the user is only capable of applying limited forces when the hand levers are wide open, whereas increased actuation forces can be supplied when the hand levers are further closed and can be grasped by one hand or with both hands.
According to German patent No. DE 199 63 097 C1 corresponding to U.S. Pat. No. 6,474,130 B2, this drawback can be reduced or eliminated by the hand lever being supported at the associated pressing jaw at its side facing the pressing jaws including a pivot joint by which the handle part of the hand lever may be pivoted into a first working position with respect to the remaining part of the hand lever being connected to the pressure lever and the pressing jaw, while the handle part in a second working position can be arranged in an angled position in the direction of the fixed hand lever with respect to the other part. Especially for great opening angles of the hand lever and thus of the pressing jaws in the second working position, the angle between the parts of the hand levers being held by one hand or by two hands of the user and thus their distance can be reduced. In this case, the pivotal connection is realized by two guiding pins being guided in suitably curved elongated channels.
According to German patent No. DE 103 46 241 B3 corresponding to U.S. Pat. No. 7,155,954 B2, this basic concept of allowing for different variable cranked designs of a hand lever has been expanded by locating a stop locking mechanism between the part of the hand lever facing the pressing jaw and the handle part of the moved hand lever. The part of the hand lever facing the pressing jaw at its end portion facing the other part of the hand lever includes a snap-in design along which a snap-in element is moved and engages suitable snap-in channels while the orientation of the pivotal connection changes. The snap-in element is designed to be subjected to the force of a spring, and it is supported with respect to the handle part of the hand lever. The use of the stop locking mechanism allows for different cranked designs of the moved hand lever being effective during different partial strokes when moving the pressing jaw from an open position into a closed position. This makes it possible to conduct separate partial strokes during the closing movement with the same distance between the handles of the hand levers. This may also be achieved by using one hand only. The pivotal connection between the two parts of the moved hand lever is realized by a joint being located at the pressure lever at the side facing away from the pressing jaws and at the part of the hand lever facing the pressing jaw. A simplified design may be attained when this joint is formed together with the joint between the front part of the moved hand lever and the associated pressing jaw. Furthermore, this prior art reference suggests to provide a partial stroke for great opening angles of the pressing jaws for which no pressing forces have to be applied by the pressure lever being movably guided between the two hand levers from its working position in an elongated hole with respect to the fixed hand lever.
Pressing pliers including two hand levers being movable with respect to one another are known from U.S. Pat. No. 4,170,154. The ends of the hand levers are connected to pressing jaws being connected to a common joint. A forced locking mechanism including additional parts is located between these two hand levers, the forced locking mechanism including a tooth segment and a pivotally supported locking tooth. The forced locking mechanism serves to reach a defined end position during the closing movement of the pressing jaws. The pressing pliers only allow for a one-step closing movement of the pressing jaws while the hand levers approach one another.
Pressing pliers having a variable adjustable jaw opening are known from U.S. Pat. No. 6,116,124. The known pliers include two hand levers being movable with respect to one another, each of the hand levers being fixedly connected to the respective pressing jaw. Some kind of a forced locking mechanism is located between the two hand levers. One of the supporting locations of the forced locking mechanism is supported to be movable by the force of a spring. Each hand lever of these pressing pliers is designed as one piece with the associated pressing jaw.
Pressing pliers in which the pressing jaws are guided to fulfil a translatory relative movement are known from German patent application No. DE 29 02 344 A1. For this purpose, one hand lever together with the fixedly connected pliers head forms a translatory guiding element for an elongated part of the movable pressing jaw. A movable hand lever is supported by a joint, the joint being stationary with respect to the fixed hand lever. A pressure lever is arranged between the movable elongated part and the movable hand lever. The pressure lever in an end portion is supported at a joint pin of the movable elongated part. At its opposite end portion, it is supported in an elongated hole of the movable hand lever at a joint pin being fixedly connected to the pressure lever. In this way, a toggle lever drive is formed by the movable elongated part, the pressure lever and the movable hand lever. Alignment of the elongated channel with respect to the components of the toggle lever drive is realized in a way that a comparatively great gear up ratio of the toggle lever drive is attained for opening and closing of the pressing pliers to allow for insertion of a pressing die. However, no pressing forces or only low pressing forces can be attained for this gear up ratio. For this opening and closing stroke, the joint pin is located in an end portion of the elongated hole, while it glides more or less quickly in the direction of the other end portion of the elongated hole during continued closing movement of the pressing pliers. Thus, different geometric conditions and different force transmission result for the toggle lever drive including the same components. The components forming the toggle lever drive remain unchanged for the above described switching step, whereby there only exist limited possibilities of attaining different gear ratios. Furthermore, relevant pressing forces can only be produced after the above described gliding movement of the joint pin from one end portion of the elongated hole into the other end portion of the elongated hole. Consequently, a pressing stroke for pressing the die only occurs in this “partial stroke”.
One single toggle lever drive is also known from German patent No. DE 198 34 859 C2. In this case, for allowing for an opening stroke and a closing stroke for which no pressing of the die is possible, the pressure lever is designed to include two parts and to be integrated in the pressing pliers such that the effective length of the pressure lever is variable during the opening stroke.
German patent No. DE 1 527 910 C corresponding to British patent No. GB 1,095,683 A discloses pressing pliers including three hand levers. Pressing of a die is attained in two partial strokes: in a first partial stroke, a first hand lever is pivoted with respect to the second and third hand lever. This results in a relative movement of two jaws with respect to one another. A die is deformed between the jaws during a first partial stroke such that it attains an oval shape. When the first partial stroke is completed, there is a relative movement between the second and third hand levers such that they approach one another. The position of the above mentioned jaws does not change during this relative movement. Instead, an additional third pressing element is moved to approach the die with respect to the above mentioned jaws depending on the movement of the second and third hand lever. This results in the oval shape of the die being deformed into a round shape. Consequently, different pressing jaws or pressing elements are used during different partial strokes.
Pressing pliers including three hand levers are also known from U.S. Pat. No. 2,283,933.